1. Field of the Invention
The invention relates to spirometers that are electrically connected to a computer through an analogue to digital converter. From the digital values every 10 milliseconds collected software calculates all the successive flow and volume values of a breathing exercise and graphically presents conventional mechanical lung functions and the related flow-volume curve, while it more particularly permutes the parameters that determine the shape of the flow-volume curve. To compute comprehensive new lung indices the figure-of-merit function of the maximum expiratory flow-volume curve, subsequently called the merit function, is developed to make quantitation of both the area under and the shape of that curve feasible. The calculated exact maximum expiratory flow-volume area under that curve, subsequently called the FV area, portrays the amount of oxygen that a person can collect. Indices developed from coefficients and exponents of the merit or the flow-volume's essential mathematical function make the hitherto impossible quantisation of the shape of the flow-volume curve workable.
Evaluation of old mechanical lung indices up to now used in pulmonary diagnostics, was complicated and not exact. Their values also differentiate poorly between distinctive lung function disorders and between lung patients and healthy people. The for the invention designed comprehensive mechanical lung indices open complete new perspectives in lung diagnostics.
2. Description of the Related Art Including Information Disclosed Under 374 CRF 1.97 and 1.98
Conventionally, in epidemiological research of lung diseases and diagnostic evaluation of patients, the forced expiratory flow-volume curve obtained by a forced breathing manoeuvre is widely used. Related lung indices, representing single points on that curve, may show flow limitation, the curve shape was visually used in the decision making process. The older lung indices do not take into account that the whole FV area represents the labor the thorax and lungs are able to achieve.
Conventional lung indices, like the forced vital capacity (FVC), the one second volume (FEV1), the FEV1/FVC ratio, the maximum mid expiratory flow rate (MMEFR), the peak flow rate (PEF or MEFR) and the average flow between two fixed volume percentages (FEF25-75%VC etc.) take into consideration only one or two points on the flow-volume curve.
They require complex pulmonary diagnostic systems, as presented by Dunning et al U.S. Pat. No. 4,296,756 and Snow et al U.S. Pat. No. 4,796,639. These diagnostic systems use several parameters and still do not differentiate successfully. The discriminant analysis of lung indices does not make a significant difference between those with severe symptoms and the relative healthy people. Only when we take the whole area under the flow-volume curve into account do these separation of the distribution curves becomes complete, as shown in the compilation of the Irian Jaya survey (see document 3).
Vermaak and others (see publication 1), used the area of a triangle in the flow-volume curve. The triangle is situated between the origin, the point of maximum volume and the point of maximum flow. To get an estimate of the area under the flow-volume curve the triangle was multiplied with an experimentally found average coefficient. The calculation of this area, however, did not use all the estimable points on the curves. The incorporation of an experimentally average coefficient, makes the calculation conditional to gender and anthropological differences, and neglect individual or disease related alterations. An area was also used for the mean transit time (MTT) because the area under a volume-time curve divided by the volume expired, gives the mean time it takes to expire. Some improvement in the discriminant analysis with conventional mechanical lung indices emerges. Calculating different areas of the curve (FIG. 7), namely after point zero, the point of reflection, and the one-second time point, gives the mean transit time of different parts of the volume-time curve (MTTN, MTTF, MTT1 respectively). The calculation gives an average time, depends only partially on the shape of the curve and gives no indication of the labor carried out to supply oxygen.
It is therefore an object of the present invention to provide the means to calculate the area under the flow-volume curve, by utilising all the digital values collected from the individual under investigation. The result is the maximum expiratory flow-volume area (MEFVA) in squares liters per second (l.sup.2 /sec). It is an exact measurement of a person's oxygen supply capacity, and is independent of the shape of the curve. It takes into account all estimable points on the curve, sampled every one hundredth of a second.
It is further an objective of the present invention, to qualify the shape of the flow-volume curve, which depend on its merit function; the function that measures the agreement between the data and the model with a particular choice of parameters.
With the merit function developed by the inventor we can model the data. However, collection of data never occurs without measurement errors. Calculations, therefore, can not be carried out with mathematical precision but have to be tested for their goodness-of-fit. As the merit function turned out to be nonlinear, we used the Levenberg-Marquardt iterative minimisation method, as described in publication 2 from Cambridge University Press 1989. The numerical calculation makes it possible to calculate the two coefficients and four exponents of the function.
The final chi-square of the numerical calculations (with this kind of function) must be lower than the number of equations minus the number of parameters (six). A chi-square, just above the norm, can still be acceptable, if the curve from the calculated formula as shown in the graphical presentation covers or fits the measured flow-volume curve. When measurement errors are not normally distributed, and inequalities are inappropriately high, but the curves cover nicely, we can still use the results. So far the parameters of the merit function have nor been used as a diagnostic tool to quantitate the shape of the flow-volume curves.
The inventor used a dry spirometer with a hinge pivoting through a vertical line, further on called the spirometer with a vertical hinge. The spirometer electronically samples digital values every hundredth of a second. The digital values are stored in an array, and represent changes in volume during the breathing exercise. The software calculates a calibration factor from the digital values before, and after, injection of two liters of air into the spirometer. Temperature and altitude readings are incorporated into the data. Flow and volume values are estimated, from this data, using a calibration factor and a body-temperature pressure-saturated (BTPS) correction factor, selected from a data base.
It would be possible to connect a `Portable Flow-Type Spirometer With Improved Accuracy` as disclosed by Hankinson et al. U.S. Pat. No. 5,277,196, instead of the dry spirometer used. Such a flow-type spirometer was not used in conjunction with the invention. It though would have made the outfit smaller but was not available by the time of the survey (1998-92). The Hankinson is more accurate than the earlier hot-wire flow-type spirometric systems that showed nonlinearity and a sensor drift.
The volume-type spirometer used in the survey maintains linearity by the arcing movements of the moving panel point being referred to a potentiometer. There is no zero drift because bellow movements begin at a start block. Hankinson claims that the updated flow-type spirometer is also linear and has no zero-drift. Consequently the systems are compatible, except for the volume which will need to be calculated from the flow values. Mobility and hardness of the flow-volume device as disclosed by Kraemer and others in U.S. Pat. No. 5,357,975, however, works at the expense of manually iterated measurements to shape a flow-volume curve. The shape, which is so important in diagnostics, deteriorates into a triangle without any guarantee that the area reflects the oxygen supply capacity.
The invention which uses a merit function of a flow-volume curve can be used, in epidemiological surveys as well as for clinical and doctor practices, and no remote controls, like in the Dunning' Remote Pulmonary Function Tester, are required. It also opens the way to supermarked self-control as done with blood pressure and cholesterol level monitors. The MEFVA gives a good qualitative prognosis of the momentary oxygen supply capacity and shows its change over time. The undimentional values from the coefficient proportionality index (CFI) and exponent proportionality indices (HPI-1 and 2), as described later, have a sharp boundary. This makes lung diagnostics much like a blood sugar level estimate in diabetes. For an explanation refer `Detailed Description of the Invention` under section h.
For clinical use in diagnosis of lung disorders and evaluation of treatment, other functions, like diffusing capacity, residual volume, resistance, alveolar volume and blood gasses, can be better judged when the supply side is defined accurately. In improved bronchial provocation tests as invented by Cloutier (U.S. Pat. No. 5,320,108) for occupational asthma, or in bronchial reactivity studies, in the clinic and by population studies (Woolcock in publication 3), the MEFVA would be of great help.
The vertical hinge of the spirometer manufactured to collect data for the investigation, obliterates the gravitational pull on the bellow in the direction of the volume extension. Garbe (U.S. Pat. No. 4,296,758) and Shipley (U.S. Pat. No. 2,999,495) have a horizontal hinge. Shipley in FIG. 4 clearly shows the influence of gravidity. The bellows, or clocks, of the volume-type spirometer as used by McKenzie (U.S. Pat. No. 642,149) moving up and down, Woldring (U.S. Pat. No. 3,889,672) and Kitrilakis (U.S. Pat. No. 3,889,660) moving sidewards around a horizontal spindle, are all subjected to gravity, which hampers their volume extension. Jones (U.S. Pat. No. 3,533,398) moving sidewards does not has the gravitational pull but needs a lot of valves to direct and thus hamper the air stream. Choksi (U.S. Pat. No. 4,635,647) used a collapsible bellow and could measure only a desired range of airflow. Valdespino et al. (U.S. Pat. No. 4,736,750) used a bellow to proceed from airflow into volume measurements but could only estimate the values FVC, FEV1 and FEV1/FVC.
Holden (U.S. Pat. No. 3,420,225) used two hinges with horizontal spindles to operate under the influence of acceleration forces going toward and being in outer space, the changes in volume measured with a potentiometer. It is obvious that the invention could not have been made with the data from a lung survey in stone age times in the Highlands of Irian Jaya with advise from several universities and without funding using equipment for outer space. Potentiometer movements of the in space used Holden invention, however, are not linear as the bellows move along an arc and do not behave as a triangle (see Description of the Preferred Embodiments). Not to mention yet the hampering friction of the bellows so near to the hinge.
Linearity and independence from gravidity are important preconditions because breathing, limited or not, is a continuous movement, and the Marquardt method can only calculate a continuous function, because it depends on six partial derivatives.
A revolving valve connecting a subject or calibrator to the spirometer or to the spirometer and ambient air also contributes to a smooth, continuous registration of the breathing movement, as no moving valves hamper the airflow like in the McKenzie version. Beaston (U.S. Pat. No. 5,004,013) made a Dripless Coupling Device and Beiter (U.S. Pat. No. 4,931,044) a Blood Collection Valve for fluids. They, however, connect one channel only and would not give the possibility to connect a spirometer to the ambient air while the subject or calibrator are still connected. This is necessary to readjust the start point, to release false pressures and to refresh the interior of the bellows. The Beason valve instead retains the fluid which is already in the apparatus. Pressure release could be done by opening the mouth peace or disconnect the calibrator, but is often not practised in every day life.
Pawelzik et al. (U.S. Pat. No. 5,190,077) made a Switchover Valve and Johnson (U.S. Pat. No. 4,470,429) a three-way valve for fluids that would put the airflow of a breathing manoeuvre into turmoil because of the sharp angles and obstruction of the rotary valves. A four-way valve of this type with the requirements of an 1.5 inch input pipe diameter for a breathing manoeuvre would not match when the spirometer was connected with one of the valves. Only the long large openings like 19 in FIG. 3 make an easy going airflow possible. Eng. E. Vanuytven from Intersoft Electronics, who invented the "MacFactory.TM." for use with the Macintosh computer, was so kind to write me the MacScoop software program in FORTH, to interface "MacFactory.TM." to collect the data.